1. Wilford, John Noble. (August 9, 2007). Fossils in Kenya Challenge Linear EvolutionNew York Times. Retrieved December 16, 2011.
2. Dalling, Robert. (2006). The Story of Us Humans, From Atoms to Today's Civilization.Lincoln: iUniverse. ISBN 0-595-391176.
3. Beck, Roger B.; Black, Linda; Krieger, Larry S.; Naylor, Phillip C.; Shabaka, Dahia Ibo. (1999). World History: Patterns of Interaction. Evanston, IL: McDougal Littell. ISBN 0-395-87274-X.
4. Boehm, Christopher. (1999). Hierarchy in the forest: the evolution of egalitarian behavior. Cambridge: Harvard University Press. p. 198. ISBN 0-674-39031-8.
5. New discovery suggests Homo erectus originated from Asia Daily News & Analysis. June 8, 2011. Retrieved December 17, 2011.
6. Moore, Matthew. (July 8, 2010). "Norfolk earliest known settlement in northern Europe." London: The Daily Telegraph Retrieved July 8, 2010.